1. Field of the Invention
The invention relates to a cam mechanism that incorporates a highly precise bearing assembly capable of significantly improving the dynamic and static positional stability of the cam mechanism""s output shaft.
2. Description of the Current Art
Various types of intermittent indexing-type cam mechanisms are currently known in the art. These cam mechanisms incorporate input and output shafts as means of transferring torque into and out of the cam mechanism, and two bearings, axially aligned with and located at each of the input and output shafts as means of supporting both thrust and radial loads applied during operation of the cam mechanism. Tapered roller bearings are generally used in cases where the input and output shafts must operate with a high degree of precision.
FIGS. 20 and 21 show cam mechanism 1a in which input shaft 4 is rotatably supported at both ends by tapered roller bearings 3 mounted in housing 2. Globoid cam 5 is axially formed on input shaft 4. Output shaft 7, whose rotating axis is offset 90-degrees in relation to that of input shaft 4, is rotatably supported by tapered roller bearings 6 mounted at both ends of the shaft and supported by housing 2. Turret 9 is installed to or integrally formed as part of output shaft 7 and incorporates cam followers 8 installed in a radial pattern on the axial perimeter of shaft 7. Turret 9 and cam followers 8 are dimensioned so as to allow cam followers 8 to mesh with spiral channel 10 of globoid cam 5. The rotation of input shaft 4 results in the rotation of output shaft 7 by means of cam followers 8 following the transverse movement of globoid cam valley 10.
FIGS. 22 and 23 illustrate the structure of cam mechanism 1b which, similar to cam mechanism 1a, incorporates input shaft 4 and output shaft 7. In cam mechanism 1b, output shaft 7 is formed as a ring-type structure that radially encompasses hollow cylindrical part 11 integrally formed at the center of housing 2. Radial and thrust loads applied to output shaft 7 are born by housing 2 as will be explained. Multiple first cam followers 12 are installed in a radial pattern on the perimeter of the inwardly facing radial surface of input shaft 7. First cam followers 12 slide along cylindrical surface 13 provided by housing 2 as means of bearing radial loads applied to input shaft 7. Second cam followers 8 are installed to the outwardly facing perimeter of output shaft 7 and are located so as to mesh with cam valley 10 of globoid cam 5. Support piece 15, structured so as not to interfere with the rotation of globoid cam 5, is installed within housing 2, and ring flange 16, formed as part of housing 2, is located radially opposite to support piece 15. Second cam followers 8 pass through the space provided between support piece 15 and ring flange 16, thus forming a structure whereby support piece 15 and ring flange 15 are able to bear the thrust loads applied to output shaft 7. Torque applied to input shaft 4 is transferred to output shaft 7 through the rotation of globoid cam 5 driving cam followers 8, thus providing a mechanism through which the desired rotational position of output shaft 7 is controlled through the rotation of input shaft 4.
Modern industry is being called upon to produce various types of components that must be made smaller and to more precise dimensions. This requirement has resulted in a demand for cam mechanisms that are able to operate with an extremely high degree of precision. It is proving difficult to make conventional cam mechanism structures operate with the degree of precision now required by many industrial applications. Even with the use of precision tapered roller bearings, conventional cam mechanisms cannot provide the high degree of operating precision called for in certain applications. This problem is the result of using standard commercial grade bearings in the construction of the cam mechanism, the difficulty of machining the housing, turret, and output shaft flanges to extremely tight tolerances, the difficulty of maintaining the required dimensions during assembly, and a general fall-off in dimensional accuracy that results from a combination of problems encountered during the manufacturing process. As a result, manufacturers often need to disassemble cam mechanisms that don""t perform to specification, check and re-machine components, and re-assemble the cam mechanism to ascertain if the required operational specifications have been met.
A major problem encountered with the use of standard roller bearings is that the bearing is unable to deliver adequate performance after being installed as a component of the cam mechanism. The following discussion will explain some of the shortcomings that can be encountered when installing a roller bearing into the cam mechanism.
1: One problem is that gap can be generated between the axial surface of output shaft (a) and the inner circumference of the bearing race. Although the perimeter of output shaft (a) and the inner diameter of race (c) may be fabricated to perfectly concentric shapes, gap (d) can exist, as illustrated in FIG. 24, after the cam mechanism is assembled as a result of the diameter of inner race (c) being fabricated to a slightly large diameter. The operating precision of the cam mechanism is thus adversely affected due to gap (d) causing the misalignment of centerline (e) of output shaft (a) with centerline (f) of bearing (b). Moreover, variations in the radial load may continually change the position of gap (d), thus creating abrasion between output shaft (a) and inner race (c), a problem that results in a shortened service life for the cam mechanism.
2: There is also a problem in that the perimeter of output shaft (a) cannot always be made to a perfectly concentric shape. In order to prevent a gap from forming between the output shaft and bearing race (see the preceding paragraph), some cam mechanisms utilize press fit tolerances in the assembly of output shaft (a) to bearing (b). As shown in FIG. 25, an eccentrically shaped cross section of output shaft (a) can be transferred the inner race (c) of bearing (b) as a result of the press fit, thus distorting bearing race surface (h) that was fabricated to the specified shape and tolerances. As a result of the distorted contours of bearing race surface (h), excessive pressure is applied to some rollers (g) while others fail to contact the race surface, thus creating an eccentric roller path that degrades the bearing""s rotating accuracy and makes it difficult for the cam mechanism to operate with a high degree of precision. Moreover, excessive pressure applied between rollers (g) and race surface (h) causes excessive wear that shortens the service life of the cam mechanism.
3: Another problem that can arise is an eccentric shape of the inner surface of race (c) that results in the inner contour of the race not accurately matching the perimeter contour of output shaft (a). FIG. 26 provides a view of bearing (b) before (FIG. a) and after (FIG. b) insertion of output shaft (a) into the bearing race. Even though output shaft (a) may be formed to perfect concentricity, inserting the output shaft into the eccentrically shaped internal diameter of race (c) will transfer the eccentric shape to the race surface (h) and thereby distort the race and bearing surface on which the rollers ride (FIG. b).
4: Furthermore, it can prove difficult to maintain an accurate 90-degree angle between output shaft (a) and seating surface (i) of bearing (b). As shown in FIG. 27, radial flange (j) is provided on output shaft (a) as means of locating bearing (b). In cases where the machining process utilized to form flange (j) leaves metal particles or other debris on the flange surface, bearing (b) will not seat completely by becoming slightly cocked on the shaft, a problem that will result in a falloff of the rotating precision of the cam mechanism""s output shaft resulting from the misalignment of center (e) of output shaft (a) and center (f) of bearing (b).
The preceding discussion explained the problems that can arise when mounting roller bearing (b) to output shaft (a). These problems can occur even when using high grade bearings, thus making it difficult to maintain precision operation of the cam mechanism""s output shaft. In light of these shortcomings, there is a pronounced need in the art for an improved bearing structure that will assure and maintain high precision operation of the cam mechanism.
The invention puts forth a structure for a cam mechanism whereby an improved bearing structure is utilized as means of obtaining highly precise dynamic rotation and static positioning of the cam mechanism""s output shaft.
The cam mechanism put forth by the invention is comprised of a cam driven rotating shaft and a cross roller bearing installed to a support structure, the cross roller bearing being provided as means of rotatably supporting the rotating shaft. Said cross roller bearing is comprised of a V-shaped outer race, a V-shaped inner race, multiple rollers located between the race parts, a roller retainer part located between the inner and outer races, and a circumferential groove, existing as the V-shaped groove of the internal or outer race, formed concentric with the rotating axis of the rotating shaft.
Because the circumferential groove can be formed in either the inner or outer race and concentrically located around the rotating axis of the rotating shaft, it becomes possible to machine the inner or outer race concentrically to the same center as the rotating shaft because the machining of the inner or outer race can be executed together with the machining of the rotating shaft itself with either one of the races attached to the rotating shaft. This structure establishes a high degree of concentricity between the bearing components and rotating shaft and thus eliminates the need to use of standard commercially available roller bearings that often exhibit defects such as imperfectly formed races and eccentrically shaped race surfaces. As the inner or outer race can be machined together in the same process applied to machine the rotating shaft, the difficulty of obtaining the desired performance from a cam mechanism using conventional roller bearings is eliminated, thus allowing the manufacture of a cam mechanism able to operate with a higher degree of precision.
An important characteristic of the invention is that the circumferential groove can be directly formed on the outer or inner perimeter of the rotating shaft simultaneously with the machining of the rotating shaft itself. During the machining process the radial center of the inner or outer races can be formed in perfect concentricity with the radial center of the rotating shaft, thus creating a bearing and rotating shaft structure capable of operating with an extremely high degree of dynamic and static precision.
A primary characteristic of the invention is that the rollers, in addition to being located between the inner and outer races, have their axial centers inclined toward the axial center of the rotating shaft, and are arranged in a radial pattern in which the axial center of each roller is inclined toward the axial center of the rotating shaft at an angle 90-degrees different than that of the adjacent roller. This structure thus allows a single cross roller bearing assembly to support both the thrust and radial loads applied to the rotating shaft during the operation of the cam mechanism. Moreover, the relatively simple construction of the cross roller bearing largely eliminates the possibility of assembly errors during manufacture of the cam mechanism. A further benefit is that the roller retainer is securely maintained in position during rotation, without any play or looseness, due to the rollers supporting the retainer through their 90-degree alternating axial centers.
The invention is characterized by the provision of oil channels formed in the inner and outer races as means of both supplying oil to and discharging oil away from the rollers.
The invention is characterized by the rotating shaft being made of a highly rigid material that, due to its minimal distortion under load, allows the inner or outer race to be machined to a high degree of concentricity in relation to the rotating shaft because either race is installed to the shaft, or be integrally machined as part of the shaft, during the machining process. This structure and process are thus able to eliminate the bearing distortion that can be encountered when using a commercially available roller bearing assembly with an imperfectly formed inner race.
The invention is characterized by the rollers being cylindrical shape with both ends being flat and in parallel alignment.
The invention is characterized by a structure in which the inner and outer races provide means of supporting and guiding the rotation of the rollers through a particular structure wherein one side of the V-shaped race contacts the load bearing surface of the roller and the other side of the race does not contact the roller, but establishes a gap between the race and the end surface of the roller. This type of roller placement provides for a highly precise low-friction rotating bearing action between the rollers and races.
The invention is further characterized by multiple pocket orifices formed within the bearing retainer part, each pocket orifice providing means of positionally maintaining a roller within the retainer part and thus allowing the rollers to rotate without mutual contact.
The internally facing edges of the pocket orifices are formed with chamfered lip parts that run along the cylindrical bearing surface of the roller installed in the retainer part. This chamfered lip part establishes a specific path through which the roller can be inserted at the appropriate angle into the retainer part, and also provides a part that positionally supports the roller within the retainer part. Moreover, the lip part eliminates the need for clearance between the internal edges of the roller pocket and the roller, thus reducing play between the rollers and retainer part and providing means whereby the cam mechanism can operate with a greater degree of precision.
The inwardly facing edge of the pocket orifice is also concave in cross section, the concave part being formed concentrically with the cylindrical bearing surface of the installed roller. The roller may come into contact with the concave edges of the pocket orifice, or else uniform clearances can be established between the roller and concave pocket edges as means of maintaining an adequate oil film for bearing lubrication, thus further enhancing the operating precision of the cam mechanism.
A further characteristic of the invention is that the outer race is formed as a ring-shaped structure that surrounds the rotating shaft which is secured to the support structure. In cases where it may be difficult to form the outer race directly into the housing, a ring shaped structure formed separately from the housing may be utilized as an aid in fabricating the outer race to a high degree of dimensional accuracy.
The separate ring-shaped structure may be formed of multiple overlapping plates that constitute the outer race, thus providing for an assembly process in which the rollers can be easily inserted between the inner and outer races supported by the retainer part there between.